1. Field of the Invention
The present invention relates to a packet forwarding apparatus having a shaping function and a bandwidth monitoring function for controlling the bandwidth of packets flowing over a network.
2. Description of the Related Art
A packet communication system used in the IP network allows a great number of users to share the same port, enabling reduction in cost per bandwidth. Because of such low cost of the packet communication system, there is a tendency to use the IP network to realize the telephone network or business network of each company conventionally implemented with a dedicated network. As such, the IP network is required to guarantee the Quality of Service (QoS) for voice data and mission critical data and to ensure High Availability, as conventionally implemented by the dedicated network.
To guarantee the QoS for the voice data and mission critical data, a packet forwarding apparatus constituting the IP network needs to have a QoS control function. For example, a shaping function is known as such QoS control function. JP-A-6-315034 (:Japanese Unexamined Patent Publication No. 6-3135034) describes a shaping apparatus for performing the shaping function. The shaping apparatus described therein has a queue for storing packets of fixed length, or cells, for each connection (VC (Virtual Connection)), and transmits the packets from the queue at a bandwidth preset for each VC, to thereby guarantee the bandwidth of each VC. The administrator of the IP network can guarantee the QoS for the voice data and mission critical data by, for example, arranging the shaping apparatus adopting such technique at a port suffering from heavy traffic load and by allocating the VC for the those data to thereby guarantee the bandwidth.
WFQ (Weighted Fair Queuing) is known as another shaping apparatus. A shaping apparatus of WFQ based on an algorithm called SCFQ (Self Clocked Fair Queuing) is described in S. Golestani, “A Self-Clocked Fair Queuing Scheme for Broadband Applications”, In proc. of INFOCOM '94, pp. 636-646, 1994. The shaping apparatus described therein controls a plurality of sessions k (k=1 to N), with weight Wk set for each session k. When a packet p_k_i arrives at the shaping apparatus, it stores the packet p_k_i in the queue, and at the same time, calculates a variable F_k_i of each packet p_k_i based on the following expression:F—k—i=L—k—i/Wk+max(F_(k−1)—i, V(ta_k_i)), where L_k_i represents a packet length of packet p_k_i, ta_k_i represents the arrival time of packet p_k_i, and V(t) represents a function for returning the value of F_k_i of the packet output from the queue at time t. At the time of outputting a packet, packet p_k_i having the smallest F_k_i is output to thereby implement packet output proportional to weight Wk of each session. The administrator of the IP network can guarantee the QoS for voice data and mission critical data by, for example, allocating one session k for the data to guarantee the bandwidth corresponding to (Wk/total sum of Wk)×port bandwidth.
As another QoS control function, a bandwidth monitoring function is known, which is described, e.g., in “Traffic Management Specification version 4.0, Chapter 4.5”, ATM Forum Technical Committee. In the CBR (Constant Bit Rate) service described therein, the maximum bandwidth (PCR: Peak Cell Rate) is contracted between networks, and the bandwidth monitoring function monitors the received cells at the maximum bandwidth, and discards any cell decided to be “non-conformant” to the contract. The administrator of the IP network can guarantee the QoS for voice data and mission critical data of a specific user by, for example, limiting the data bandwidth for each user by means of the bandwidth monitoring function provided at a node at the entrance of the network, to thereby eliminate an influence of data of one user on voice data and mission critical data of another user.
Meanwhile, as means for ensuring High Availability in the switches, a link aggregation technique for handling a plurality of physical ports (physical links) as one logical Link Aggregation Group and enabling the Link Aggregation Group to be treated as if it were a single physical port is described in “Link Aggregation according to IEEE standard 802.3ad” (refer to http://www.itworld.com/Net/1750/NWW001113tech/pfindex.html). With this technique, even if one physical port in the Link Aggregation Group is in failure, at least one physical port remains normal, which prevents interruption in communication between switches connected via the Link Aggregation Group. Thus, the administrator of the IP network can improve availability of the network by changing the single port connecting the switches to a plurality of ports aggregated by the Link Aggregation.
Further, as means for ensuring High Availability in a MPLS (Multi Protocol Label Switching) network where paths called LSP (Label Switching Paths) are set, a Fast Rerouting technique is described in “Fast Reroute Extensions to RSVP-TE for LSP Tunnels”, IETF RFC 4090. The document describes a one-to-one backup method system and a facility backup method system for protecting traffic over the LSP. In the one-to-one backup method system, one backup LSP is set corresponding to a LSP to be protected (hereinafter referred to as “protected LSP”). In the facility backup method system, one backup LSP is set for a plurality of protected LSP. When a failure occurs in the protected LSP, the traffic on the relevant LSP is detoured to the backup LSP. The administrator of the IP network can improve the availability of the network by setting a backup LSP for a protected LSP to enable such detour at the time of failure of the protected LSP.